1. Field
The following description relates to an optical pickup capable of implementing a tracking servo that is compatible with multiple types of optical information storage media.
2. Description of Related Art
In order to implement a tracking servo, an optical pickup may split light into zeroth-order light and first-order light by transmitting the light through a grating, and may perform an operation on signals which are obtained by detecting the zeroth-order light and the first-order light.
In the case of using a grating that has a diffraction grating pattern on a single side, a spacing between zeroth-order light and first-order light is typically determined for a single disc type such as a digital versatile disc (DVD), a spacing between zeroth-order light and first-order light for a compact disc (CD) is determined according to wavelength characteristics. However, because a refractive index for a wavelength of the light for CD (i.e. infrared light) is smaller than a refractive index for a wavelength of the light for DVD (i.e. red light) a spacing between zeroth-order light and first-order light diffracted from the grating is greater in the light for CD than in the light for DVD.
As the zeroth-order light and the first-order light for DVD are closer to each other on the optical information storage medium, eccentric characteristics become easier to view. However, in a DVD dual layer (DL) disc, an increase of a parasitic curve in an S-curve may cause recognition limitation. Due to the recognition limitation, it is necessary to maintain a predetermined distance between the zeroth-order light and the first-order light. However, the predetermined spacing between the zeroth-order light and the first-order light for the DVD deteriorates eccentric disc characteristics of the CD.